1. Field of the Invention
This invention relates to a two-cycle internal combustion engine and more particularly to a two-cycle engine having three, or a multiple of three, cylinders and, in each cylinder, intake and exhaust valves operated in response to a crank angle.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 48-51126 discloses a two-cycle engine having a sub chamber for forming a rich mixture in a scavenging passage between a cylinder chamber and a crank chamber. A one-way (reed) valve is provided in the scavenging passage between the sub chamber and the crank chamber. However, this known two-cycle engine does not have multiple cylinders and does not intend to prevent the air/gas from flowing from the exhaust system back to the intake system, which may happen particularly in a two-cycle three cylinder engine provided with air charging effects, due to exhaust pulsation among the cylinders. Therefore, this two-cycle engine does not provide an individual one-way valve for each cylinder.
A six-cylinder two-cycle engine is already known in which the exhaust systems in the respective cylinders are divided into two groups, each group including the exhaust systems of three cylinders in which the piston strokes are conducted at each phase of 120.degree. C., to ensure that a high output power is obtained by the air charging effects due to exhaust pulsation among the cylinders, which effects are particularly distinctive in a three-cylinder two-cycle engine.
In a known four-cycle engine, such as disclosed, for example, in Japanese Examined U.M. Publication No. 59-22250, a reed valve is provided in an intake port to prevent fresh air in a cylinder chamber from flowing back to the intake port. However, this known engine pertains to a four-cycle engine and, therefore, air charging effects due to exhaust pulsation, as mentioned above, cannot be expected and the valve timings of the intake and exhaust valves are quite different from those of a two-cycle engine.